Introduction

We reported previously that the mouse has a strong defense system against kidney crystal deposition. By investigating subtle genetic differences between mice substrains C57BL/6J(B6J) and C57BL/6N(B6N), we identified nicotinamide nucleotide transhydrogenase (Nnt) as a new kidney stone candidate gene to elucidate the possibility of inhibiting kidney stone formation. Here, we focused on this cellular disorder.

Methods

Eight-week-old male B6J and B6N mice (n = 15 in each group) were used in this study. Renal calcium oxalate monohydrate crystal deposition was induced with a daily intra-abdominal injection of 80 mg/kg glyoxylate for 12 days. Every 6 days, animals were euthanized and renal specimens were collected. Kidney cross-sections were observed by polarized-light optical microphotography, and crystal regions with strong birefringence were measured and expressed as percentages of the total tissue area of the renal cross-section, using NIH Image software. Total RNA was isolated from glyoxylate-treated kidneys and reverse-transcribed into double-stranded cDNA. In another study, renal specimens were fixed with methacarn and reactive oxygen species (ROS) activity was investigated using a Carbonyl Protein Immunostaining Kit®. In addition, the changes in oxidative stress in the kidney, using superoxide dismutase-1 (SOD-1) and malondialdehyde (MDA) as markers, were compared by immunostaining and western blotting.

Results

Numerous kidney crystal depositions in the renal tubules were detected in both B6J and B6N mice. The number of crystal depositions was greatest after 12 days of treatment, and the crystal count was 16.2-fold higher in B6J mice than in B6N mice. ROS activity in the kidney revealed strong activity throughout the kidney tissue and a slightly higher tendency in B6J. SOD-1 and MDA expression in the kidney was observed in the renal tubular epithelial cells and did not differ significantly between the B6J and B6N mice.

Conclusions

The decreased expression of Nnt observed in B6J mice is also present in humans. Nnt expression reduces intracellular ROS in the mitochondria. ROS is increased by decreased Nnt expression, while kidney stone formation is predicted to be promoted. Although the findings of this study showed the same tendency, it was not possible to recognize a clear difference between the sub-systems. Further analysis of the Nnt gene may facilitate elucidation of the pathogenesis of kidney stones.

Funding

none